Traditional machining techniques, such as, tube drawing, grinding, and polishing are used to fabricate needles. While satisfactory for simple needle designs, these techniques cannot be used to fabricate more sophisticated features and geometries that provide extended functionality. For example, a needle with two fluid channels to allow the simultaneous injection of two fluids to the same area is very difficult to fabricate with traditional needle machining techniques. Electronic circuitry, such as, electrodes and amplification circuitry may be used for charge delivery, electric field sensing, or electrophoretic pumping. Biological sensors to provide, for example, biological assay capability, would be extremely useful. Insertion and extraction limiting barbs are also potentially very useful. Additionally, a pump built into the needle and multiple inlet and outlet ports are highly desirable features. A dual prong needle would allow delivery through one prong and sensing in the other. These features are very difficult to implement with traditional machining.
Recently, silicon microfabrication techniques have been used to construct hypodermic needles. For example, microfabrication processes to produce needles are described in the work by Chen and Wise (J. Chen et al., "A Multichannel Neural Probe for the Selective Chemical Delivery at the Cellular Level", Solid State Sensor and Actuator Workshop, Hilton Head, S.C., 1994) and also by Linn (Liwei L. Linn, et al., "Silicon Processed Microneedles", Technical Digest, 7th International Conference on Solid-State Sensors and Actuators, Transducers '93, Yokohama, Japan, Jun. 7-10, 1993). There are two drawbacks with this early work. First, the disclosed processes are destructive to the wafer from which the needles are produced. Second, the processes do not rely upon a mold. Thus, new wafers must be used each time the process is repeated. This results in considerable added expense.
Single mold processes to make needles are known in the art. For example, the HexSi process invented by Chris Keller (Christopher G. Keller et al., "Nickel-Filled HexSi Thermally Actuated Tweezers", Technical Digest, Transducers 95, Stockholm, Sweden, Jun. 25-29, 1995, pp. 376-379) is a single wafer micromolding process. Unfortunately, the Hexsil process can only form relatively short needles (generally less than a millimeter).
In view of the foregoing, it would be highly desirable to provide an improved technique for fabricating hypodermic needles. Ideally, the technique would allow the fabrication of needles with extended functionality, such as multiple fluid channels, multiple ports, and integrated circuitry. In addition, the technique would preferably avoid prior art problems of limited needle length. Ideally, the technique would provide a re-usable mold process to reduce fabrication expense.